Sulfidation Impacts on the Hydrophobicity of Stepped Iron Surfaces

Abstract

Nanoscale zero‐valent iron (nZVI) has demonstrated high potential for the remediation of contaminated groundwater. Its lifetime is directly related to the hydrophobicity of nZVI. A promising approach to enhance the lifetime of nZVI is through sulfidation. Herein, the density functional theory (DFT) is applied to understand the impact of sulfidation on the hydrophobicity of stepped Fe surfaces. Adsorption properties of sulfur (S) at different coverages on the flat Fe(110) and stepped Fe(210) and Fe(211) surfaces are investigated. Sulfur has the stronger adsorption at a low surface coverage due to limited S–S repulsion. At the highest coverage (⊖ = 1 ML) on Fe(210) and Fe(211), the atoms at the step edges catalyze the formation of iron sulfides. The DFT results show surface hydrophobicity is mainly determined by the S coverage. At the low S coverage, the surface may become more hydrophilic due to the enhanced adsorption strength of water on the surface. However, an increase in the S coverage can efficiently block water adsorption, which is further evidenced by ab initio molecular dynamics (AIMD) results. The findings show that controlling S coverages is essential to engineer the hydrophobicity of nZVI surfaces for practical water remediation applications.

The impact of metal dopants on the properties of nZVI: a theoretical study

“…The optPBE exchange-correlation energy was employed considering the vdW interaction correction [39][40][41][42]. The OptPBE vdW correction method was chosen because it has been shown in our previous studies to accurately represent the electronic and magnetic properties of Fe [35]. The electron-ion interactions were described using the PAW potentials, with the 3s 2 3p 6 3d 7 4s 1 , 2s 2 2p 4 , 1s 1 , 4s 2 3d 9 , 4s 2 3d 8 , 4d 10 and 4d 10 5s 1 treated as valence electrons of Fe, O, H, Cu, Ni, Pd, and Ag, respectively [43].…”

“…To our knowledge, no theoretical research has been conducted on metal-doped stepped Fe surfaces and their interaction with water. The stepped surfaces can be used to replicate the properties of nZVI because Fe atoms with low coordination numbers (CNs) at the edge of the stepped surface are more reactive than those on the flat Fe (110) surface [33][34][35]. These reactive Fe atoms on the stepped surface easily adsorb water molecules and dissociate them with a low-energy barrier.…”

Tailoring Fe0 Nanoparticles via Lattice Engineering for Environmental Remediation

“…The chemical properties of nonmetal p-block elements themselves also affect the physicochemical properties of latticedoped nFe 0 . It has been both experimentally and theoretically proved that lattice S in Fe 0 crystals could induce hydrophobicity, which originates from the hydrophobic nature of S. 43,58 As compared to a S atom sit on an Fe(110) plane, a lattice S atom in Fe( 110) is more hydrophobic and can block more nearby Fe sites for H adsorption with a relatively smaller H binding energy. 18 Theoretical calculations show lattice N and P in a Fe (110) plane can provide hydrophobicity as that of lattice S. 59 Even incorporation of N into nFe 0 could improve the materials' hydrophobicity and electron transfer, providing efficient and selective trichloroethylene (TCE) degradation, despite the N being present as crystalline Fe 4 N rather than being incorporated into the Fe crystal.…”

Impacts of Perfluoroalkyl Substances on Aqueous and Nonaqueous Phase Liquid Dechlorination by Sulfidized Nanoscale Zerovalent Iron

“…Sulfidized nanoscale zerovalent iron (S-nFe 0 ) has been recognized as a better version than nFe 0 for groundwater remediation. − Sulfidation can alter the physicochemical properties of nFe 0 particles (e.g., accelerated electron transfer, increased hydrophobicity, and inhibited H adsorption) by changing their geometric and electronic structure, thereby improving the materials’ performance for contaminant reductions. − The reactivity and selectivity of S-nFe 0 with TCE could be increased to 3–54 times and 9–160 times higher than those of nFe 0 , respectively. ,, Both S content and S speciation are crucial factors that determine the structure–property–activity relationships of materials, and S speciation plays a more significant role in the hydrophobicity of materials compared to S content. ,,, Meanwhile, PFASs could be adsorbed by nFe 0 and S-nFe 0 through hydrophobic and electrostatic interactions, which were affected by the properties of PFASs and the surface corrosion products of nFe 0 particles . However, it is unclear how coexisting PFASs affect TCE degradation by S-nFe 0 or if S speciation could change this effect.…”